Abstract

We demonstrate the use of a microwave hairpin resonator to measure the time-dependent, phase-resolved electron number density in ionizationwaves. Under our argon glow discharge conditions, the instability was caused by two-step ionization; and the wave frequency depended on the volume quenching rate of the metastable states. We measured the metastable state density using diode laser absorption. The peak electron number density lagged behind the peak metastable state density by 60°. This phase shift reveals the nonlocal nature of the electron kinetics due to two-step ionization.